1. Field of the Invention
This invention relates to a process for producing L-phenylalanine and, more particularly, to a process for producing L-phenylalanine which comprises allowing a microorganism which belongs to the genus Nocardia and is capable of producing L-phenylalanine from phenylpyruvic acid or a salt thereof and an amino group donor to act upon an aqueous solution containing phenylpyruvic acid or a salt thereof and an amino group donor in a hydrogen gas atmosphere.
2. Description of the Related Art
So-far known processes for producing L-phenylalanine from phenylpyruvic acid or a salt thereof and an amino group donor using a microorganism or an enzyme derived therefrom include, among others, (1) processes comprising allowing the culture broth obtained by cultivating a bacterium belonging to the genus Alcaligenes or Pseudomonas, for instance, in a nutrient medium, living or dried cells isolated from such culture broth or phenylpyruvate transaminase obtained from the culture broth of a fungus belonging to the genus Aspergillus, Penicillium or the like to act upon a mixture containing phenylpyruvic acid and an amino group donor such as L-aspartic acid, L-glutamic acid or the like (cf. Japanese Patent Publications Nos. 10672/62 and 20556/70), (2) processes comprising effecting the enzymatic transamination between L-glutamic acid and phenylpyruvic acid by using cultured cells of a bacterium belonging to the genus Escherichia, Proteus or Clostridium, for instance, a sonicate or an extract of said cells, each having enzymatic activities of hydrogenase, L-glutamate dehydrogenase and transaminase, in the presence of a nitrogen source and in a hydrogen gas atmosphere so that L-phenylalanine can be prepared through L-glutamic acid by execution of L-glutamic acid formation and transamination in such manner that the substrate may be conjugative (cf. U.S. Pat. No. 3,183,170 and Japanese Patent Publication No. 1995/65), (3) processes comprising reacting phenylpyruvic acid with ammonia in the presence of a compatible source of reducing equivalents such as glucose and in the presence of the culture of a bacterium belonging to the genus Escherichia or Enterobacter, among others, and capable of producing dehydrogenase and transaminase (cf. European Patent Publication No. 140,503) and (4) processes comprising reacting phenylpyruvic acid with an ammonium ion source such as ammonium chloride in the presence of nicotinamide-adenine dinucleotide and in the presence of L-phenylalanine dehydrogenase obtained from the strain Brevibacterium species DSM2448 (cf. U.S. Pat. No. 4,590,161).
Those microorganisms or enzymes derived therefrom which are actually known to be usable in producing L-phenylalanine from phenylpyruvic acid and an amino group donor have been limited to bacteria or enzymes derived from bacteria or fungi, as mentioned above. It would be desirable if the microorganism to be used in producing L-phenylalanine could be selected from within a broader range of microorganisms.
From such point of view, several reseachers inclusive of one of the present inventors have previously found that L-phenylalanine can be produced by allowing a microorganism belonging to the genus Nocardia which is capable of producing L-phenylalanine from phenylpyruvic acid or a salt thereof and an amino group donor to act upon an aqueous solution containing phenylpyruvic acid or a salt thereof and an amino group donor (cf. Japanese Patent Application Laid-Open No. 56088/86). When this process is used, it is possible to produce L-phenylalanine from phenylpyruvic acid or a salt thereof and a variety of amino group donors in good yields and in a simple and easy manner. Nevertheless, it would be more preferable if L-phenylalanine could be produced more efficiently.